1. Field of the Invention
The present invention relates to a field of disk drives which perform read/write operations of data on a disk medium rotated by a spindle motor. In particular, it relates to a motor control technique under a low-temperature environment.
2. Description of the Related Art
Generally, disk storages, represented by hard disk drives (also “disk drives”) are configured to perform data read/write operations, using a head (magnetic head), on a disk medium (hereinafter “disk”) rotated at high speed by a spindle motor.
In recent years, fluid dynamics bearing motors having stable rotation characteristic have been adopted. Fluid dynamics bearing motors use oil or the like as the bearing, and thus have a characteristic that the power consumption depends on the viscosity of the oil. Specifically, if the temperature lowers, the viscosity of the oil increases, and the power consumption amount (current consumption amount) relatively increases to maintain a rated rotation number.
In the meantime, in particular, small disk drives are gaining popularity as external memories for notebook personal computers, personal digital assistances (PDAs), and digital apparatuses mounted on vehicles, etc. Therefore, the temperature range under which disk drives are used is broadened, thus they may be used under a low-temperature environment.
In consideration of use of disk drives under such a low-temperature environment, if a fluid dynamics bearing motor is adopted as a spindle motor, a power consumption amount relatively increases, and thus it is required to increase a maximum allowable power (current) of the whole drive.
If a disk drive is designed on the premise that it is used under a low-temperature environment, there is a problem that the maximum allowable power (current) of the whole device increases since adopting a fluid dynamics bearing spindle motor increases the current consumption amount. Specifically, if the maximum allowable power increases, a power supply circuit and a motor driver of a large capacity are required, which is inappropriate for a small-size disk drive required to reduce the power consumption. For example, for a motor driver which performs boosting using an inductor, the maximum current influences the size of the inductor, and thus there occurs a problem that it is difficult to mount the inductor on a printed circuit board.
Conventionally, as means for inhibiting the increase in spindle motor power consumption, a method of providing a temperature sensor and heater in the vicinity of the fluid dynamics bearing portion has been proposed. When the temperature sensor senses a change to a low temperature, driving the heater to generate heat (refer to, for example, Jpn. Pat. Appln. KOKAI Pub. No. 6-4988).
This art is aimed at heating the oil used as the fluid dynamics bearing in a low temperature to relatively reduce the viscosity of the oil. However, this method requires providing a temperature sensor and a heater in the vicinity of the bearing of the spindle motor, and a circuit for controlling the heater. This complicates the structure around the motor and raises the number of components, thus also the cost. Further, this method has a problem that disk start-up is delayed, since the drive cannot operate until the oil of the bearing portion reaches a certain temperature by a heater.